The present invention relates to a method of molding a resin coated bearing, in which method a coating member made of a synthetic resin is insert-molded onto an outer peripheral surface of a metallic outer race of a ball bearing, a method of manufacturing a resin coated bearing, and a resin coated bearing molded by the molding method.
Conventionally, there is, for example, a guide roller for vehicular sliding doors, to which a resin coated bearing is applied. By the way, with vehicular sliding doors, an upper guide roller provided on an upper portion of a front end of a sliding door, a center guide roller provided centrally of a rear end in a heightwise direction, and a lower guide roller provided on a lower portion of the front end are caused to engage rollingly with an upper rail provided on an upper edge of an opening of a vehicle body, a center rail provided centrally of a rear side wall of the vehicle body adjacent to the opening of the vehicle body in the heightwise direction, and a lower rail provided on a lower edge of the opening of the vehicle body to support the sliding door slidably along a side wall of the vehicle body, thus enabling sliding the sliding door to open and close.
JP-A-2003-176661 shows an example, in which a bearing type roller with a synthetic resin coated on an outer periphery of an outer race is used as a guide roller for sliding doors. For the reason why such bearing type guide roller is used, there is a disadvantage that in the case where a guide roller constructed as a resin solid roller with a small number of parts is used, the resin solid roller is abraded locally by a load of a sliding door and smooth rotation is obstructed whereby the resin solid roller is broken and the sliding door comes off a vehicle body in the worst case. On the other hand, since at least a structure of a roller in a bearing type guide roller comprises an outer race made of metal (bearing steel), there is an advantage that the roller itself is hard to crack and a sliding door is hard to come off a vehicle body even when a resin part is broken.
However, the resin coated bearing shown in JP-A-2003-176661 is not described in detail but as far as the specification and drawings (FIG. 4) thereof are referred to, it is found that there is involved a disadvantage that since in insert-molding of a synthetic resin onto an outer race of the bearing, the plural point gate system (for example, three point gate system) is used to inject a molten resin into a cavity of forming dies, a weld portion (a portion where molten resins injected from different gates combine together in the cavity) is reduced in strength and generation of crack starts from the weld portion at the time of high loading. Hereupon, it is conceivable to insert-mold a synthetic resin onto an outer race of a bearing in the film gate system shown in, for example, JP-A-08-142112.